Due to the lead time and expense required to design and build new multi-speed automatic transmissions, some motor vehicles are equipped with an auxiliary or “add-on” gearbox to provide one or more additional gear ratios. Some motor vehicles use this auxiliary gearbox to compound the gear ratios provided by the conventional automatic transmission so as to provide the additional gear ratios. Typically, such “compounders” include a planetary gearset and one or more clutches and/or brakes that can be selectively actuated to establish a direct drive mode and either of an underdrive ratio mode or an overdrive ratio mode. As is known, the direct drive mode provides a one-to-one gear ratio. On the other hand, the ratio drive modes provide a gear ratio other than one-to-one which, in conjunction with the multiple speed ratios established by the automatic transmission, provides a simple and relatively inexpensive means for establishing additional drive gears.
With reference to FIG. 8, a prior art compounder assembly 8 will be described. To manufacture compounder assembly 8, a first bore B1 is drilled into an input shaft for carrying fluid at a first pressure. A second bore B2 is drilled into the input shaft for carrying fluid at a second pressure. Typically, first bore B1 is adapted to carry fluid for influencing clutch actuation during a gearshift event while the second bore B2 carries fluid for lubrication. While such compounders have proven to work satisfactorily for their intended purpose, a need exists to minimize complexity while advancing the state of the art.